Retatrutide vs Tirzepatide: Dual vs Triple Agonists Explained
Tirzepatide hits two hormone receptors and is an approved medicine. Retatrutide adds a third and is still in trials. This guide compares their structure, receptors, half-life and status, with semaglutide for context.
The one-line difference
Tirzepatide is a dual agonist of the GIP and GLP-1 receptors. Retatrutide is a triple agonist that adds the glucagon receptor. Both come from Eli Lilly, both are modified peptides with a fatty-acid side chain, and both are built for once-weekly use in clinical settings.
Comparison table
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptors | GLP-1 | GIP + GLP-1 | GIP + GLP-1 + glucagon |
| Developer | Novo Nordisk | Eli Lilly | Eli Lilly |
| Half-life (approx.) | 7 days | 5 days | 6 days |
| Australian status | TGA approved | TGA approved (Mounjaro) | Not approved |
| Our research vials | Not stocked | 10mg | 5mg to 60mg |
- Semaglutide1
- Tirzepatide2
- Retatrutide3
- Semaglutide~7 d
- Retatrutide~6 d
- Tirzepatide~5 d
Approximate published values. All three are designed for once-weekly dosing in trials.
What is tirzepatide?
Tirzepatide is a 39-amino-acid peptide based on the GIP hormone sequence, engineered to also activate the GLP-1 receptor. A fatty-acid chain lets it bind albumin, giving it a half-life of about five days. It is approved in Australia under the brand name Mounjaro; the TGA added a chronic weight management indication in September 2024, alongside its type 2 diabetes use.
- Developer
- Eli Lilly
- Class
- GIP / GLP-1 dual agonist
- Length
- 39 amino acids
- Brand (AU)
- Mounjaro
- Half-life
- About 5 days
What does the glucagon arm add?
Glucagon is usually thought of as the hormone that raises blood sugar, so adding it can seem counter-intuitive. In metabolic research, though, glucagon receptor signalling is studied for its effects on energy expenditure and liver fat. Retatrutide balances that against strong GLP-1 and GIP activity. Whether the third pathway produces meaningfully different outcomes is exactly what the phase 3 trials are designed to show. More in what is retatrutide.
Status and availability
Tirzepatide is an approved prescription medicine in Australia. Retatrutide is not approved anywhere yet; Lilly plans to file with the US FDA in early 2027. See is retatrutide available in Australia? for the full timeline. Research-grade versions of both are sold for laboratory use only.
Handling in the lab
Both research peptides are supplied as lyophilised powder and reconstituted with bacteriostatic water. The reconstitution guide includes a worked example.
Further reading
For laboratory research use only. Not for human consumption. Not medical or legal advice.
